Essentially, you must add a Registry Entry which is spelled out below:

[HKEY_CURRENT_USERSoftwareValveSteam]
"LastContentProviderURL"=-

You can also download a zip file with that entry below. Open the zip file, copy to your computer and open the file. Windows will give a prompt asking if you really want to add the information to the registry. Hit "Yes".

After adding this you will be able to play Counter-Strike with Internet Explorer 7.